A base station or a repeater has an antenna for transmission and reception, and one test point for measuring the performance of the antenna is the voltage standing-wave ratio (VSWR).
The VSWR represents a voltage ratio measured from an adjacent node and amplitude within a cable or a waveguide having a standing wave, or the VSWR denotes the ratio of maximum to minimum voltage in a standing wave pattern in a transmission line.
For example, a progressive wave is divided into a progressive wave and a reflected wave on two media with two different kinds of impedance because of impedance mismatch, and the difference between the two waves represents the VSWR which is defined in Math FIG. 1 when the reflection coefficient is given to be p.
                              V          ⁢                                          ⁢          S          ⁢                                          ⁢          W          ⁢                                          ⁢          R                =                              1            +                                        ρ                                                          1            -                                        ρ                                                                        Math        ⁢                                  ⁢        Figure        ⁢                                  ⁢        1            
That is, a VSWR of 1 represents that line impedance and end impedance are completely matched and incident waves are passed through the media, and the VSWR is an important factor for checking the antenna operation status since the greater the VSWR becomes the more incident waves are reflected therefrom.
FIG. 1 shows a conventional VSWR measuring system.
As shown, a base station 10 has a diversity antenna for receiving and identifying signals which are transmitted through various spatial and temporal paths of radio frequency (RF) propagation between a base station and an antenna, and improving received characteristics. The base station 10 includes a transmission and receiving circuit 11, a diversity receiving circuit 16, a first antenna 15, and a second antenna 19. The first antenna 15 is used to transmit and receive signals and the second antenna 19 is used to receive signals. For ease of description, the first antenna 15 is established to be a transmit antenna and the second antenna 19 is established to be a receive antenna. A process for measuring the respective transmission and receiving VSWRs will now be described.
A transmitter (not illustrated) of the transmission and receiving circuit 11 outputs transmission signals to the first antenna 15 through a high power amplifier 13, and a receiver (not illustrated) thereof receives signals through a low noise amplifier 14. A duplexer 12 connects a transmission circuit and a receiving circuit so that the first antenna 15 may be used for transmitting and receiving signals.
A receiving circuit 16 includes a band-pass filter 18 for selecting a desired channel from the RF signals received from the second antenna, and a low noise amplifier 17.
A conventional VSWR measuring system includes a transmitted VSWR measurer 30, a received VSWR measurer 40, and directional couplers 21 and 22. The directional couplers 21 and 22 are installed in the first antenna 15 and the second antenna 19 and respectively output a signal corresponding to one direction to a port.
Therefore, a signal transmitted to the first antenna by the transmission circuit 11 is transmitted to the transmitted VSWR measurer 30 through a path of (b), and a power signal which is not output to the first antenna but is reflected is transmitted to the transmitted VSWR measurer 30 through a path of (a). Therefore, the VSWR of the transmit antenna is calculated by Math FIG. 1 by using power signals of the incident wave and the reflected wave.
The received VSWR measurer 40 includes a power signal receiver 41 and a power signal output unit 42. A test signal generated by the power signal output unit 42 is passed through a path of (d) having passed through the directional coupler 22 to the power signal receiver 41. A test signal generated by the received VSWR measurer 40 and reflected on the second antenna 19 is transmitted to the power signal receiver 41 through a path of (c). The power signal receiver 41 receives the power signals provided through the paths of (d) and (c), and a processor in the received VSWR measurer 40 uses the power signals to calculate a received VSWR.
As described, the prior art uses an additional VSWR measurer to obtain signal information on the progressive wave and the reflected wave used for the VSWR. However, it is needed to consider length and substance of a repeater feeder of a base station and a level of an output signal in order to produce an accurate VSWR. Also, it is inevitable that VSWRs must be measured multiple times since a level of the output signal is steeply varied depending on a call state while the base station provides a service. Hence, it is required for the VSWR measurer to include an additional memory and a central processing unit for measuring the VSWR multiple times and amending the same according to characteristics of the base stations.
Further, it is required for a user to visit each base station to be measured and test the same when the conventional VSWR measurer is used. In addition, a large amount of cost is generated for installing a VSWR measurer in each base station, integrated management in consideration of the characteristics of the base station is difficult, and it is impossible to determine the antenna's status in real-time.